Eidolon Purple Clear vs Arianrhod Blue

How close are they?

ΔE 22.4, loose: different enough that you should pick on purpose. Arianrhod Blue is a little darker, more muted, cooler than Eidolon Purple Clear.

Can I use Arianrhod Blue instead of Eidolon Purple Clear?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Arianrhod Blue is a little darker, more muted, cooler than Eidolon Purple Clear.

Can I use Eidolon Purple Clear instead of Arianrhod Blue?

The same difference applies the other way round: Eidolon Purple Clear is a little lighter, more saturated, warmer.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.